Use effective columns when cells with colspan are present.

Source/modules/accessibility/AXTableColumn.cpp

 /*
  * Copyright (C) 2008 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 83 matching lines @@
 
     LayoutTable* table = toLayoutTable(renderer);
     LayoutTableSection* tableSection = table->topSection();
     for (; tableSection; tableSection = table->sectionBelow(tableSection, SkipEmptySections)) {
         unsigned numRows = tableSection->numRows();
         for (unsigned r = 0; r < numRows; r++) {
             LayoutTableCell* layoutCell = tableSection->primaryCellAt(r, m_columnIndex);
             if (!layoutCell)
                 continue;
 
-            // Whenever cell's col is less then current column index, we've found the cell with colspan.
+            // Whenever cell's effective col is less then current column index, we've found the cell with colspan.
             // We do not need to add this cell, it's already been added.
-            if (layoutCell->col() < m_columnIndex)
+            if (layoutCell->table()->colToEffCol(layoutCell->col()) < m_columnIndex)
                 continue;
 
             AXObject* cell = axObjectCache()->getOrCreate(layoutCell->node());
             if (!cell || !cell->isTableCell())
                 continue;
 
             if (toAXTableCell(cell)->scanToDecideHeaderRole() == ColumnHeaderRole)
                 headers.append(cell);
         }
     }
@@ skipping 57 matching lines @@
 
     LayoutTableCell* cell = 0;
     // also account for cells that have a span
     for (int testCol = m_columnIndex; testCol >= 0; --testCol) {
         LayoutTableCell* testCell = section->primaryCellAt(0, testCol);
         if (!testCell)
             continue;
 
         // we've reached a cell that doesn't even overlap our column
         // it can't be our header
-        if ((testCell->col() + (testCell->colSpan()-1)) < m_columnIndex)
+        if (testCell->table()->colToEffCol(testCell->col() + (testCell->colSpan()-1)) < m_columnIndex)
             break;
 
         Node* node = testCell->node();
         if (!node)
             continue;
 
         if (thTagRequired && !node->hasTagName(thTag))
             continue;
 
         cell = testCell;
@@ skipping 32 matching lines @@
         // make sure the last one isn't the same as this one (rowspan cells)
         if (m_children.size() > 0 && m_children.last() == cell)
             continue;
 
         m_children.append(cell);
         m_columnRect.unite(cell->elementRect());
     }
 }
 
 } // namespace blink